Coating system, articles and assembly using the same and methods of reducing sticktion

ABSTRACT

The present invention provides a coating system for an article including a first component having a surface in frictional engagement with a surface of a second component, wherein at least a portion of at least one surface of the component(s) is coated with a coating prepared from a composition including a first, curable organopolysiloxane comprising at least two alkenyl groups; and a second, curable organopolysiloxane comprising at least two polar groups, the second organopolysiloxane being different from the first organopolysiloxane, which can provide low breakloose force when used in syringe assemblies.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of and claims priority to U.S.patent application Ser. No. 11/693,249, filed Mar. 29, 2007, whichclaims priority to provisional application No. 60/787,366 filed on Mar.30, 2006, which are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a coating system for an article, such as asyringe assembly, comprising curable organopolysiloxane(s), methods toreduce static and kinetic friction between slidable surfaces, andarticles of low friction prepared thereby.

2. Description of Related Art

Certain devices require slow and controlled initiation and maintenanceof sliding movement of one surface over another surface. It is wellknown that two stationary surfaces having a sliding relationship oftenexhibit sufficient resistance to initiation of movement that graduallyincreased pressure applied to one of the surfaces does not causemovement until a threshold pressure is reached, at which point a suddensliding separation of the surfaces takes place. This sudden separationof stationary surfaces into a sliding relationship is herein referred toas “breakout”.

A less well known, but important frictional force is “breakloose force”,which refers to the force required to overcome static friction betweensurfaces of a syringe assembly that has been subjected to autoclavingand may have a slight deformation in one or both of the contactingsurfaces of the syringe assembly, for example in the syringe barrel. Inaddition to autoclaving, parking of the assembly can further increasethe breakloose force.

Breakout and breakloose forces are particularly troublesome in liquiddispensing devices, such as syringes, used to deliver small, accuratelymeasured quantities of a liquid by smooth incremental line to lineadvancement of one surface over a graduated second surface. The problemis also encountered in devices using stopcocks, such as burets, pipets,addition funnels and the like where careful dropwise control of flow isdesired.

The problems of excessive breakout and breakloose forces are related tofriction. Friction is generally defined as the resisting force thatarises when a surface of one substance slides, or tends to slide, overan adjoining surface of itself or another substance. Between surfaces ofsolids in contact, there may be two kinds of friction: (1) theresistance opposing the force required to start to move one surface overanother, conventionally known as static friction, and (2) the resistanceopposing the force required to move one surface over another at avariable, fixed, or predetermined speed, conventionally known as kineticfriction.

The force required to overcome static friction and induce breakout isreferred to as the “breakout force”, and the force required to maintainsteady slide of one surface over another after breakout or breakloose isreferred to as the “sustaining force”. Two main factors contribute tostatic friction and thus to the breakout or breakloose force. The term“stick” as used herein denotes the tendency of two surfaces instationary contact to develop a degree of adherence to each other. Theterm “inertia” is conventionally defined as the indisposition to motionwhich must be overcome to set a mass in motion. In the context of thepresent invention, inertia is understood to denote that component of thebreakout force which does not involve adherence.

Breakout or breakloose forces, in particular the degree of stick, varyaccording to the composition of the surfaces. In general, materialshaving elasticity show greater stick than non-elastic materials,particularly when the surfaces are of dissimilar composition. The lengthof time that surfaces have been in stationary contact with each otheralso influences breakout and/or breakloose forces. In the syringe art,the term “parking” denotes storage time, shelf time, or the intervalbetween filling and discharge. Parking generally increases breakout orbreakloose force, particularly if the syringe has been refrigeratedduring parking.

A conventional approach to overcoming breakout has been application of alubricant to a surface to surface interface. Common lubricants used arehydrocarbon oils, such as mineral oils, peanut oil, vegetable oils andthe like. Such products have the disadvantage of being soluble in avariety of fluids, such as vehicles commonly used to dispensemedicaments. In addition, these lubricants are subject to air oxidationresulting in viscosity changes and objectionable color development.Further, they are particularly likely to migrate from the surface tosurface interface. Such lubricant migration is generally thought to beresponsible for the increase in breakout force with time in parking.

Silicone oils are also commonly used as lubricants. They are poorsolvents and are not subject to oxidation, but migration and stick dooccur, and high breakout forces are a problem. Polytetrafluoroethylenesurfaces provide some reduction in breakout forces, but this material isvery expensive, and the approach has not been totally effective.

Thus there is a need for a better system to overcome high breakout andbreakloose forces whereby smooth transition of two surfaces fromstationary contact into sliding contact can be achieved.

SUMMARY OF THE INVENTION

In some embodiments, the present invention provides a coating system foran article comprising a first component having a surface in frictionalengagement with a surface of a second component, wherein at least aportion of at least one surface of the component(s) is coated with acoating prepared from a composition comprising:

(a) a first, curable organopolysiloxane comprising at least two alkenylgroups; and

(b) a second, curable organopolysiloxane comprising at least two polargroups, the second organopolysiloxane being different from the firstorganopolysiloxane.

In some embodiments, the present invention provides articles ofmanufacture, such as syringe assemblies, having the coating system ofthe present invention applied to at least one surface of the article ofmanufacture that is in frictional engagement with another surface of thearticle of manufacture.

In some embodiments, the present invention provides a method forlubricating the interface between a first component having a surface infrictional engagement with a surface of a second component, comprisingthe steps of:

(a) applying the coating system according to the present invention to atleast a portion of at least one surface of the component(s) to form acoating upon the portion of the surface; and

(b) irradiating the coating of step (a) to at least partially cure thecoating.

In some embodiments, the present invention provides a method forreducing breakout and/or sustaining forces of slidable surfaces in theinterior of a syringe assembly comprising:

(a) applying a coating system according to the present invention to theinterior wall of the syringe barrel to form a coating thereon; and

(b) irradiating the coating of step (a) to at least partially cure thecoating.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will best be understood from the followingdescription of specific embodiments when read in connection with theaccompanying drawings:

FIG. 1 is a graph of infusion pump actuation force test results at afeed rate of 10 ml/hr for a prior art syringe assembly;

FIG. 2 is a graph of infusion pump actuation force test results at afeed rate of 10 ml/hr for a syringe assembly according to the presentinvention;

FIG. 3 is a graph of infusion pump actuation force test results at afeed rate of 1.0 ml/hr for a syringe assembly according to the presentinvention;

FIG. 4 is a graph of infusion pump actuation force test results at afeed rate of 0.1 ml/hr for a syringe assembly according to the presentinvention;

FIG. 5 is a graph of infusion pump actuation force test results at afeed rate of 1.0 ml/hr for a syringe assembly according to the presentinvention;

FIG. 6 is a graph of infusion pump actuation force test results at afeed rate of 10 ml/hr for a syringe assembly according to the presentinvention;

FIG. 7 is a graph of infusion pump actuation force test results at afeed rate of 0.1 ml/hr for a syringe assembly according to the presentinvention;

FIG. 8 is a graph of infusion pump actuation force test results at afeed rate of 1.0 ml/hr for a syringe assembly according to the presentinvention;

FIG. 9 is a graph of infusion pump actuation force test results at afeed rate of 10 ml/hr for a syringe assembly according to the presentinvention;

FIG. 10 is a graph of infusion pump actuation force test results at afeed rate of 0.1 ml/hr for a syringe assembly according to the presentinvention;

FIG. 11 is a graph of infusion pump actuation force test results at afeed rate of 1.0 ml/hr for a syringe assembly according to the presentinvention; and

FIG. 12 is a graph of infusion pump actuation force test results at afeed rate of 10 ml/hr for a syringe assembly according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Other than in the operating examples, or where otherwise indicated, allnumbers expressing quantities of ingredients, reaction conditions, andso forth used in the specification and claims are to be understood asbeing modified in all instances by the term “about.” Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Furthermore, when numerical ranges ofvarying scope are set forth herein, it is contemplated that anycombination of these values inclusive of the recited values may be used.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between andincluding the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

The present invention provides a coating system for an articlecomprising a first component having a surface in frictional engagementwith a surface of a second component. In accordance with the system andmethods of the invention, the force required to achieve breakout,breakloose and/or sustaining forces can be greatly reduced, wherebytransition of surfaces from stationary contact to sliding contact occurswithout a sudden surge. When breakout or breakloose is complete and thesurfaces are in sliding contact, they slide smoothly upon application ofvery low sustaining force. Substantially less lubricant may be requiredand lubricant migration is reduced or eliminated. The effect achieved bythe system and methods of the present invention can be of long duration,and articles, such as syringes, can retain the advantages of lowbreakout, breakloose and sustaining forces throughout any parkingperiod. When the surfaces are part of a liquid dispensing device, smallhighly accurate increments of liquid may be dispensed repeatedly withoutsudden surges. Thus, a syringe treated according to the method of theinvention can be used to administer a medicament to a patient withoutthe danger of surges whereby accurate control of dosage and greatlyenhanced patient safety are realized.

Non-limiting examples of articles that can be treated with the coatingsystem of the present invention include articles comprising a firstcomponent having a surface in frictional engagement with a surface of asecond component, including for example medical devices such as syringeassemblies, syringe pumps, drug cartridges, needleless injectors, liquiddispensing devices and liquid metering devices. In some embodiments, themedical device is a syringe assembly comprising a first component whichis a syringe barrel and a second component which is a sealing member.

The first component of the coating system can be formed from glass,metal, ceramic, plastic, rubber or combinations thereof. In someembodiments, the first component is prepared from one or more olefinicpolymers, such as polyethylene, polypropylene, poly(1-butene),poly(2-methyl-1-pentene) and/or cyclic polyolefin. For example, thepolyolefin can be a homopolymer or a copolymer of an aliphaticmonoolefin, the aliphatic monoolefin preferably having about 2 to 6carbon atoms, such as polypropylene. In some embodiments, the polyolefincan be basically linear, but optionally may contain side chains such asare found, for instance, in conventional, low density polyethylene. Insome embodiments, the polyolefin is at least 50% isotactic. In otherembodiments, the polyolefin is at least about 90% isotactic instructure. In some embodiments, syndiotactic polymers can be used. Anon-limiting example of a suitable cyclic polyolefin includes anethylene-norbornene copolymer such as TOPAS® ethylene-norbornenecopolymer commercially available from Ticona Engineering Polymers ofFlorence, Ky.

The polyolefin can contain a small amount, generally from about 0.1 to10 percent, of an additional polymer incorporated into the compositionby copolymerization with the appropriate monomer. Such copolymers may beadded to the composition to enhance other characteristics of the finalcomposition, and may be, for example, polyacrylate, polyvinyl,polystyrene and the like.

In some embodiments, the first component may be constructed of apolyolefin composition which includes a radiation stabilizing additiveto impart radiation stability to the container, such as a mobilizingadditive which contributes to the radiation stability of the container,such as for example those disclosed in U.S. Pat. Nos. 4,959,402 and4,994,552, assigned to Becton, Dickinson and Company and both of whichare incorporated herein by reference.

The second component can be formed from any material such as isdiscussed above for the first component, but preferably is formed froman elastomeric material. Elastomers are used in many important andcritical applications in medical devices and pharmaceutical packaging.As a class of materials, their unique characteristics, such asflexibility, resilience, extendability, and sealability, have provenparticularly well suited for products such as catheters, syringe tips,drug vial articles, injection sites, tubing, gloves and hoses. Threeprimary synthetic thermoset elastomers typically are used in medicalapplications: polyisoprene rubber, silicone rubber, and butyl rubber. Ofthe three rubbers, butyl rubber has been the most common choice forarticles due to its high cleanness and permeation resistance whichenables the rubber to protect oxygen- and water-sensitive drugs.

Suitable butyl rubbers useful in the method of the present inventioninclude copolymers of isobutylene (about 97-98%) and isoprene (about2-3%). The butyl rubber can be halogenated with chlorine or bromine.Suitable butyl rubber vulcanizates can provide good abrasion resistance,excellent impermeability to gases, a high dielectric constant, excellentresistance to aging and sunlight, and superior shock-absorbing andvibration-damping qualities to articles formed therefrom.

Other useful elastomeric copolymers include, without limitation, styrenecopolymers such as styrene-butadiene (SBR or SBS) copolymers,styrene-isoprene (SIS) block polymers or styrene-isoprene/butadiene(SIBS), in which the content of styrene in the styrene block copolymerranges from about 10% to about 70%, and preferably from about 20% toabout 50%. The rubber composition can include, without limitation,antioxidants and/or inorganic reinforcing agents to preserve thestability of the rubber composition.

In some embodiments, the second component can be a sealing member, suchas a stopper, O-ring, plunger tip or piston. Syringe plunger tips orpistons typically are made of a compressible, resilient material such asbutyl rubber, because of the vulcanized rubber's ability to provide aseal between the plunger and interior housing of the syringe. Syringeplungers, like other equipment used in the care and treatment ofpatients, have to meet high performance standards, such as the abilityto provide a tight seal between the plunger and the barrel of thesyringe.

The coating is applied to at least a portion of at least one surface ofthe component(s) in frictional engagement with an opposed surface ofanother component. In some embodiments, at least a portion of at leastone surface of the component(s) is coated with the coating. In otherembodiments, at least a portion of a surface of the first component andat least a portion of a surface of the second component are coated withthe coating. In some embodiments in which the first component isprepared from a non-cyclic polyolefin, the portion of the surface of thefirst component is uncoated, and the portion of the surface of thesecond component is coated with the coating. In some embodiments inwhich the syringe barrel is prepared from polypropylene and the sealingmember is prepared from butyl rubber, the surface of the syringe barrelis uncoated and the at least one portion of the surface of the sealingmember is coated with the coating. In other embodiments in which thesyringe barrel is prepared from polypropylene and the sealing member isprepared from butyl rubber, the at least one portion of the surface ofthe sealing member can be coated with the coating. Methods for coatingthe surface(s) are discussed in detail below.

The coating system of the present invention comprises a cured coatingprepared from a composition comprising one or more first, curableorganopolysiloxane(s) comprising at least two alkenyl groups and one ormore second, curable organopolysiloxane(s) comprising at least two polargroups, as described below. As used herein, the term “cure” as used inconnection with a composition, e.g., a “cured composition” or a “curedcoating” shall mean that at least a portion of the crosslinkablecomponents which form the composition are at least partiallycrosslinked. As used herein, the term “curable”, as used in connectionwith a component of the composition, means that the component hasfunctional groups capable of being crosslinked, for example alkenylgroups such as vinyl groups. In certain embodiments of the presentinvention, the crosslink density of the crosslinkable components, i.e.,the degree of crosslinking, ranges from 5% to 100% of completecrosslinking. One skilled in the art will understand that the presenceand degree of crosslinking, i.e., the crosslink density, can bedetermined by a variety of methods, such as dynamic mechanical thermalanalysis (DMTA) using a TA Instruments DMA 2980 DMTA analyzer conductedunder nitrogen. This method determines the glass transition temperatureand crosslink density of free films of coatings or polymers. Thesephysical properties of a cured material are related to the structure ofthe crosslinked network.

As discussed above, the coating system of the present inventioncomprises a cured coating prepared from a composition comprising one ormore first, curable organopolysiloxane(s) comprising at least twoalkenyl groups. Each alkenyl group of the first organopolysiloxane (a)can be independently selected from the group consisting of vinyl, allyl,propenyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl anddecenyl. One skilled in the art would understand that the firstorganopolysiloxane (a) can comprise one or more of any of the abovetypes of alkenyl groups and mixtures thereof. In some embodiments, atleast one alkenyl group is vinyl. Higher alkenyl or vinyl contentprovides more efficient crosslinking.

In some embodiments, the first organopolysiloxane (a) can be representedby the following structural formulae (I) or (II):

wherein R is alkyl, haloalkyl, aryl, haloaryl, cycloalkyl,silacyclopentyl, aralkyl, fluoro, fluoroalkyl, and mixtures thereof; Xis about 60 to about 1000, preferably about 200 to about 320; and y isabout 3 to about 25. Copolymers and mixtures of these polymers are alsocontemplated.

Non-limiting examples of useful first organopolysiloxanes (a) include:vinyldimethyl terminated polydimethylsiloxanes; vinylmethyl,dimethylpolysiloxane copolymers; vinyldimethyl terminated vinylmethyl,dimethylpolysiloxane copolymers; divinylmethyl terminatedpolydimethylsiloxanes; polydimethylsiloxane, mono vinyl, monon-butyldimethyl terminated; and vinylphenylmethyl terminatedpolydimethylsiloxanes.

In some embodiments, a mixture of siloxane polymers selected from thoseof Formulae I and/or II can be used. For example, the mixture cancomprise two different molecular weight vinyldimethylsilyl terminatedpolydimethylsiloxane polymers, wherein one of the polymers has anaverage molecular weight of about 5,000 to about 25,000 and preferablyabout 16,000, and the other polymer has an average molecular weight ofabout 30,000 to about 75,000 and preferably about 38,000. Generally, thelower molecular weight siloxane can be present in amounts of about 20%to about 80%, such as about 60% by weight of this mixture; and thehigher molecular weight siloxane can be present in amounts of about 80%to about 20%, such as about 40% by weight of this mixture.

Another non-limiting example of a suitable first organopolysiloxane (a)is (7.0-8.0% vinylmethylsiloxane)-dimethylsiloxane copolymer,trimethylsiloxy terminated, such as VDT-731 vinylmethylsiloxanecopolymer which is commercially available from Gelest, Inc. ofMorrisville, Pa.

In some embodiments, the first organopolysiloxane (a) can furthercomprise one or more fluoro groups, such as —F or fluoroalkyl groupssuch as trifluoromethyl groups.

In some embodiments, the first organopolysiloxane (a) can furthercomprise one or more alkyl and/or one or more aryl groups, such asmethyl groups, ethyl groups or phenyl groups, respectively.

Generally, the viscosity of the alkenyl-substituted siloxanes can rangefrom about 200 to about 1,000,000 cst.

In some embodiments, the first organopolysiloxane (a) comprises about 10to about 80 weight percent of the composition. In other embodiments, thefirst organopolysiloxane (a) comprises about 15 to about 50 weightpercent of the composition. In other embodiments, the firstorganopolysiloxane (a) comprises about 20 to about 40 weight percent ofthe composition.

While not wishing to be bound by any theory, it is believed that thealkenyl functional siloxanes can increase the viscosity of the coatingand improve binding between the coating and the coated surface.

The composition also comprises one or more second, curableorganopolysiloxane(s) comprising at least two polar groups, the secondorganopolysiloxane(s) being different from the firstorganopolysiloxane(s), for example having different types of atom(s) ordifferent numbers of atoms in the respective organopolysiloxanes.

Each polar group of the second organopolysiloxane (b) is independentlyselected from the group consisting of acrylate, methacrylate, amino,imino, hydroxy, epoxy, ester, alkyloxy, isocyanate, phenolic,polyurethane oligomeric, polyamide oligomeric, polyester oligomeric,polyether oligomeric, polyol, carboxypropyl, and fluoro groups. Oneskilled in the art would understand that the second organopolysiloxane(b) can comprise one or more of any of the above polar groups andmixtures thereof. Preferably, these organopolysiloxanes are notmoisture-curable.

In some embodiments, the polar groups are acrylate groups, for exampleacryloxypropyl groups. In other embodiments, the polar groups aremethacrylate groups, such as methacryloxypropyl groups.

The organopolysiloxane having polar groups can further comprise one ormore alkyl groups and/or aryl groups, such as methyl groups, ethylgroups or phenyl groups.

A non-limiting example of a suitable organopolysiloxane (b) is [15-20%(acryloxypropyl)methylsiloxane]-dimethylsiloxane copolymer, such asUMS-182 acrylate functional siloxane which is commercially availablefrom Gelest, Inc. of Morrisville, Pa. Other useful organopolysiloxanes(b) include polyfluoroalkylmethyl siloxanes and fluoralkyl, dimethylsiloxanecopolymers.

In other embodiments, the second organopolysiloxane (b) can berepresented by the formula (III):

wherein R₁ is selected from the group consisting of acrylate,methacrylate, amino, imino, hydroxy, epoxy, ester, alkyloxy, isocyanate,phenolic, polyurethane oligomeric, polyamide oligomeric, polyesteroligomeric, polyether oligomeric, polyol, carboxypropyl, and fluorogroups; and R₂ is alkyl, n ranges from 2 to 4, and x is an integersufficient to give the lubricant a viscosity of about 10 to 2,000,000cst.

In some embodiments, the second organopolysiloxane (b) comprises about 1to about 40 weight percent of the composition. In other embodiments, thesecond organopolysiloxane (b) comprises about 3 to about 20 weightpercent of the composition. In other embodiments, the secondorganopolysiloxane (b) comprises about 1 to about 20 weight percent ofthe composition.

While not wishing to be bound by any theory, it is believed that thepolar siloxanes may be present on top of the coated surface to helpreduce the coefficient of friction between the engaged surfaces. Also,after irradiation, it is believed that the viscosity of the polarsiloxane may increase and improve the binding of the coating tosubstrate.

In some embodiments, the composition further comprises one or moreorganopolysiloxane(s) different from the first and secondorganopolysiloxanes, for example siloxanes of Formula (IV) shown below,such as alkyl siloxanes, and/or organopolysiloxanes comprising at leasttwo pendant hydrogen groups.

Non-limiting examples of such organopolysiloxanes can be represented bythe following structural formula (IV):

wherein R is alkyl, haloalkyl, aryl, haloaryl, cycloalkyl,silacyclopentyl, aralkyl and mixtures thereof; and Z is about 20 toabout 1,800. In some embodiments, the organopolysiloxanes of Formula(IV) can be represented by the following structural formula (IVA):

wherein Z can be as above, or for example can be about 70 to about 1800or about 70 to about 1,350. The average molecular weight of theorganopolysiloxane of Formula (IV) can be about 1900 to about 100,000,and preferably about 5,000 to about 100,000. Generally, this correspondswith a viscosity of about 20 to about 300,000 centistokes (cst).

A non-limiting example of a suitable alkyl organosiloxane ispolydimethylsiloxane. The viscosity of the alkyl organosiloxane canrange from about 100 to about 1,000,000 cst, and in some embodiments canrange from about 12,500 to about 100,000 cst. In some embodiments, thealkyl organosiloxane comprises about 1 to about 20 weight percent of thecomposition. In other embodiments, the alkyl organosiloxane comprisesabout 1 to about 10 weight percent of the composition. In otherembodiments, the alkyl organosiloxane comprises about 1 to about 5weight percent of the composition.

Non-limiting examples of suitable organopolysiloxanes comprising atleast two pendant hydrogen groups include organopolysiloxanes havingpendant hydrogen groups along the polymer backbone or terminal hydrogengroups. In some embodiments, the organopolysiloxane can be representedby the following structural formulae (V):

wherein p is about 8 to about 12, for example about 10. In otherembodiments, the organopolysiloxane can be represented by the followingstructural formula (VI):HMe₂SiO(Me₂SiO)_(p)SiMe₂H  (VI)wherein p is about 140 to about 170, for example about 150 to about 160.A mixture of these polymers can be used comprising two differentmolecular weight materials. For example, about 2% to about 5% by weightof the mixture of a trimethyl silyl terminatedpolymethylhydrogensiloxane having an average molecular weight of about400 to about 7,500, for example about 1900, can be used in admixturewith about 98% to about 95% of a dimethylhydrogen silyl-terminatedpolymethylhydrogensiloxane having an average molecular weight of about400 to about 37,000 and preferably about 12,000. In some embodiments,the mole ratio of vinyl groups to hydrogen groups in the reactivecomponent is about 0.010:1 to about 0.20:1. In some embodiments, themole ratio of hydrogen groups of the crosslinking polymer to hydrogengroups of the chain-extending polymer is about 5.0:1 to about 20:1.Non-limiting example of useful organopolysiloxanes comprising at leasttwo pendant hydrogen groups include dimethylhydro terminatedpolydimethylsiloxanes; methylhydro, dimethylpolysiloxanecopolymers;methylhydro terminated methyloctyl siloxane copolymers; and methylhydro,phenylmethyl siloxane copolymers.

In some embodiments, the hydrogen organopolysiloxane can furthercomprise one or more fluoro groups, such as —F or fluoroalkyl groupssuch as trifluoromethyl groups.

In some embodiments, the hydrogen organopolysiloxane can furthercomprise one or more alkyl and/or one or more aryl groups, such asmethyl groups, ethyl groups or phenyl groups, respectively.

Generally, the viscosity of the hydrogen organopolysiloxane can rangefrom about 100 to about 1,000,000 cst.

In some embodiments, the hydrogen organopolysiloxane comprises about 1to about 40 weight percent of the composition. In other embodiments, thehydrogen organopolysiloxane comprises about 5 to about 30 weight percentof the composition. In other embodiments, the hydrogenorganopolysiloxane comprises about 10 to about 30 weight percent of thecomposition.

In some embodiments, the composition is essentially free ofmoisture-curable siloxanes, for example a moisture-curable siloxanecomprising at least two hydroxyl groups, such as for example:

wherein R₂ is alkyl, n ranges from 2 to 4, and x is an integersufficient to give the lubricant a viscosity of about 10 to 2,000,000cst. Other moisture-curable siloxanes which have moisture-curingcharacter as a result of functionality include siloxanes havingfunctional groups such as: alkoxy, aryloxy; oxime; epoxy; —OOCR₁₃,N,N-dialkylamino; N,N-dialkylaminoxy; N-alkylamido; —O—NH—C(O)—R₁₃;—O—C(═NCH₃)—NH—CH₃, —O—C(CH₃)═CH₂; and —S—C₃H₆Si(OCH₃)₃; wherein R₁₃ isH or hydrocarbyl. As used herein, “moisture-curable” means that thesiloxane is curable at ambient conditions in the presence of atmosphericmoisture. As used herein, “essentially free of moisture-curablesiloxanes” means that the composition includes less than about 5 weightpercent of moisture-curable siloxanes, in some embodiments less thanabout 2 weight percent, and in other embodiments is free ofmoisture-curable siloxanes.

In accordance with the methods of the invention, surfaces which have asliding relationship with each other are treated with the coating systemof the present invention which is cured. The coating system of theinvention may be applied to any surface which slides in contact withanother surface. Application of a film of coating to the slidingsurfaces may be accomplished by any suitable method, as, for example,dipping, brushing, spraying and the like. The lubricant may be appliedneat or it may be applied in a solvent, such as low molecular weightsilicone, non-toxic chlorinated or fluorinated hydrocarbons, forexample, 1,1,2-trichloro-1,2,2-trifluoroethane, freon or conventionalhydrocarbon solvents such as alkanes, toluene, petroleum ether and thelike where toxicology is not considered important. The solvent issubsequently removed by evaporation. The lubricant film may be of anyconvenient thickness and, in practice, the thickness will be determinedby such factors as the viscosity of the lubricant and the temperature ofapplication. For reasons of economy, the film preferably is applied asthinly as practical, since no significant advantage is gained by thickerfilms.

The inventive compositions can be fully cured after application orpartially cured to attach them to the substrate, and then fully cured ata later time. For example, air drying will permit partial cure. Thecompositions are initially fluid and can be applied directly to thesubstrate in any suitable manner, for example by dipping, brushing orspraying. The exact thickness of the coating does not appear to becritical and very thin coatings, e.g., one or two microns exhibiteffective lubricating properties. While not necessary for operability,it is desirable that the thickness of the coating be substantiallyuniform throughout.

Curing of the reactive portion can be accomplished by conventionalmethods well known in the art. For example, curing by use of a catalyst,heat curing via oven or radio frequency (RF) are useful methods as wellas the use of gamma, e-beam or ultraviolet radiation. Any mechanismwhich will initiate the hydrosilylation reaction is a useful curingtechnique.

In some embodiments, the coating is at least partially cured byirradiation with an isotope or electron beam. Radiation sterilization inthe form of ionizing radiation commonly is used in hospitals for medicaldevices such as catheters, surgical items and critical care tools. Gammairradiation is the most popular form of radiation sterilization andtypically is used when materials are sensitive to the high temperatureof autoclaving but are compatible with ionizing radiation. Thebactericidal effect of gamma irradiation exerts its microbicidal effectby oxidizing biological tissue, and thus provides a simple, rapid andefficacious method of sterilization. Gamma rays are used either from acobalt-60 (⁶⁰Co) isotope source or from a machine-generated acceleratedelectron source. Sufficient exposures are achieved when the materials tobe sterilized are moved around an exposed ⁶⁰Co source for a definedperiod of time. The most commonly used validated dose for sterilizingmedical devices is about 10 to about 100 kGy, for example 20-50 kGy.

In some embodiments, the composition further comprises a catalyticamount of a catalyst for promoting crosslinking of the firstorganopolysilaxane (a) and the second organopolysiloxane (b).Non-limiting examples of suitable catalysts for promoting heat cureinclude platinum or rhodium group metal catalysts, such as Karstedtcatalyst Pt₂{[(CH₂═CH)Me₂Si]₂O}₃ or peroxide catalysts, such as dicumylperoxide. The catalyst can be present in an amount ranging from about0.001 to about 0.05 weight percent of the composition.

In the case of oven curing, temperatures should range from about 150° toabout 180° C. and residence time in the oven is generally about 30 toabout 40 seconds, depending on the precise formulation. If RF techniquesare used, the coil should conduct enough heat to obtain a substratesurface temperature of about 180° to about 240° C. At thesetemperatures, only about 2 to about 4 seconds are required for cure. Ifgamma radiation techniques are used, the need for hydrosilylationinitiating catalyst is eliminated, since the radiation will start thecure. This technique has the advantage of sterilizing as well, which isuseful in medical applications.

In some embodiments, the coated articles are subjected to asterilization treatment. Many sterilization techniques are availabletoday to sterilize medical devices to eliminate living organisms such asbacteria, yeasts, mold and viruses. Commonly used sterilizationtechniques used for medical devices include autoclaving, ethylene oxide(EtO) or gamma irradiation, as well as more recently introduced systemsthat involve low-temperature gas plasma and vapor phase sterilants.

One common sterilization technique is steam sterilization orautoclaving, which is a relatively simple process that exposes a device,for example, to saturated steam at temperatures of over 120° C. for aminimum of twenty minutes at a pressure of about 120 kPa. The process isusually carried out in a pressure vessel designed to withstand theelevated temperature and pressure to kill microorganisms by destroyingmetabolic and structural components essential to their replication.Autoclaving is the method of choice for sterilization of heat-resistantsurgical equipment and intravenous fluid as it is an efficient,reliable, rapid, relatively simple process that does not result in toxicresidues.

Thus, in some embodiments, the present invention provides a method forlubricating the interface between a first component having a surface infrictional engagement with a surface of a second component, comprisingthe steps of: (a) applying a coating system according to claim 1 to atleast a portion of at least one surface of the component(s) to form acoating upon the portion of the surface; and (b) irradiating the coatingof step (a) to at least partially cure the coating.

In other embodiments, the present invention provides a method forreducing breakout force of a surface adapted for slidable engagementwith another surface comprising: (a) applying a coating system accordingto claim 1 to at least a portion of at least one surface to form acoating upon the portion of the surface; and (b) irradiating the coatingof step (a) to at least partially cure the coating.

In other embodiments, the present invention provides a method forreducing sustaining force of a surface adapted for slidable engagementwith another surface comprising: (a) applying a coating system accordingto claim 1 to at least a portion of at least one surface to form acoating upon the portion of the surface; and (b) irradiating the coatingof step (a) to at least partially cure the coating.

In other embodiments, the present invention provides a method forreducing breakout and sustaining forces of slidable surfaces in theinterior of a syringe assembly comprising: (a) applying a coating systemaccording to claim 1 to the interior wall of the syringe barrel to forma coating thereon; and (b) irradiating the coating of step (a) to atleast partially cure the coating.

Breakout forces, breakloose forces and sustaining forces may beconveniently measured on a universal mechanical tester or on a testingmachine of the type having a constant rate of cross-head movement, as,for example an Instron model 1122, as described in detail below.

The present invention is more particularly described in the followingexamples, which are intended to be illustrative only, as numerousmodifications and variations therein will be apparent to those skilledin the art.

EXAMPLES Example 1

In this example, 10 ml syringe components were coated with aconventional polydimethylsiloxane or a coating composition according tothe present invention, subjected to irradiation, and evaluated forbreakloose force and infusion pump actuation force (sticktion) relatingto pump performance.

Each syringe barrel was lubricated with a conventionalpolydimethylsiloxane having a viscosity of 12,500 est. Helvoet FM457butyl rubber syringe stoppers were coated with a conventionalpolydimethylsiloxane having a viscosity of 100,000 cst (“Control”) or acoating composition according to the present invention (“Formulation A”)consisting of 20 weight percent of VDT-731 (7.0-8.0%vinylmethylsiloxane)-dimethylsiloxane copolymer, trimethylsiloxyterminated, available from Gelest, Inc. of Morrisville, Pa., 5 weightpercent of UMS-182 [15-20%(acryloxypropyl)methylsiloxane]-dimethylsiloxane copolymer, availablefrom Gelest, Inc., and 75 weight percent of DC 360 polydimethylsiloxanehaving a viscosity of about 100,000 est, available from NuSil.

Each component was irradiated with cobalt at 45 kGy. Each syringe wasassembled and filled with 10 ml of saline solution available from VWRProducts and autoclaved at 124° C. for 30 minutes.

The breakloose force (in Newtons) of each sample syringe to simulatefast speed injection was determined by an Instron Model No. 1122 incompression (injection) mode using a 50 kg compression load cell at across head speed of 100 mm/min. The breakloose force is visuallydetermined as the highest peak of the curve or point of where the slopeof the curve changes on the graph. The minimum sustaining force isdetermined as the lowest or smooth section of the curve after thebreakloose force. The maximum sustaining force is determined as thehighest section of the curve after the breakloose force. The valuesreported in Table 1 below are the average of five samples for each ofSample A (coated with Formulation A) and the Control.

The infusion pump actuation force and fluid delivery characteristics foreach test syringe were evaluated using a Becton Dickinson Program 2eight pump data acquisition system. Each syringe is filled with 10 nilof Deionized water. All air bubbles in the syringe were removed and theplunger rod was advanced until the sealing rib of the stopper coincidedwith the desired test volume marking on the scale. Microbore tubing(0.020″ ID×60″ length) was connected to the syringe and the other endwas connected to a 23 gauge×1 inch length needle. The needle wasinserted into a beaker. The tubing set was manually filled with waterfrom the syringe and the syringe was mounted in the pump. The flange ofthe barrel connected the front of the flange slot. The syringe plungerrod was positioned against the syringe pusher. There was no gap betweenthe load cell and the plunger rod. The pump was purged by setting theflow rate at the maximum speed allowed by the pump. Once fluid isflowing freely through the tubing and needle into the beaker, thespecified flow rate was set on the pump and infusion was begun. A chartof force over time for each syringe was generated, as shown in FIGS.1-3. A visual determination of sticktion or no sticktion was made byviewing each chart for the smoothness of the curve. A smooth curveindicated no sticktion and an irregularly-shaped curve (for example withdiscernable peaks) indicated sticktion.

TABLE 1 Sample A Control Breakloose Force 23 ± 1 36 ± 1 (N) PumpActuation  1.0 ml/hr: no sticktion  1.0 ml/hr: no sticktion Force 10.0ml/hr: no sticktion 10.0 ml/hr: sticktion

As shown in Table 1 above, Sample A coated with a coating systemaccording to the present invention exhibit lower breakloose force andreduced sticktion, even at 10.0 ml/hr pumping conditions.

Example 2

In this example, 10 ml syringe components were evaluated in the samemanner as in Example 1 above, however the syringe barrel was formed fromcyclic polyolefin. Both the stopper and barrel were coated as in Example1 and each component was irradiated with cobalt at 20 kGy. Each syringewas assembled and filled with 10 ml of deionized water and autoclaved at124° C. for 30 minutes. The test results reported in Table 2 below arean average of the test results for five samples each. The infusion pumpactuation force test results are shown in FIGS. 4-6.

TABLE 2 Sample A Control Breakloose Force 15 ± 1 49 ± 1 (N) PumpPerformance  0.1 ml/hr: no sticktion  0.1 ml/hr: sticktion  1.0 ml/hr:no sticktion  1.0 ml/hr: no sticktion 10.0 ml/hr: no sticktion 10.0ml/hr: sticktion

As shown in Table 2 above, Sample A coated with a coating systemaccording to the present invention exhibit lower breakloose force andreduced sticktion at 0.1 ml/hr pumping conditions.

Example 3

In this example, 10 ml syringe components were evaluated in the samemanner as in Example 1 above, the syringe barrel being formed from thecyclic polyolefin. Each stopper was coated with 100,000 cstpolydimethylsiloxane. Each barrel was coated with a coating ofFormulation B consisting of 20 weight percent of VDT-731 (7.0-8.0%vinylmethylsiloxane)-dimethylsiloxane copolymer, trimethylsiloxyterminated, 10 weight percent of UMS-182 [15-20%(acryloxypropyl)methylsiloxane]-dimethylsiloxane copolymer, and 70weight percent of DC 360 polydimethylsiloxane having a viscosity ofabout 100,000 cst (“Sample B”); or Formulation C consisting of 20 weightpercent of VDT-731 (7.0-8.0% vinylmethylsiloxane)-dimethylsiloxanecopolymer, trimethylsiloxy terminated, 20 weight percent of UMS-182[15-20% (acryloxypropyl)methylsiloxane]-dimethylsiloxane copolymer, and60 weight percent of DC 360 polydimethylsiloxane having a viscosity ofabout 100,000 cst (“Sample C”). Each component was irradiated withcobalt at 20 kGy. Each syringe was assembled and filled with 10 ml ofdeionized water and autoclaved at 124° C. for 30 minutes. The testresults reported in Table 3 below are an average of the test results forfive samples each. The infusion pump actuation force test results areshown in FIGS. 7-12.

TABLE 3 Sample B Sample C Breakloose Force 16 ± 1 15 ± 1 (N) PumpPerformance  0.1 ml/hr: no sticktion  0.1 ml/hr: no sticktion  1.0ml/hr: no sticktion  1.0 ml/hr: no sticktion 10.0 ml/hr: no sticktion10.0 ml/hr: sticktion

As shown in Table 3 above, Samples B and C coated with a coating systemaccording to the present invention exhibit low breakloose force and nosticktion at 0.1, 1.0 and 10 ml/hr pumping conditions.

Example 4

In this example, 10 ml syringe components were evaluated in the samemanner as in Example 1 above, the syringe barrel being formed frompolypropylene. Each stopper was coated with 100,000 cstpolydimethylsiloxane. Each barrel was coated with a coating of aformulation as shown in Table 4. Sample Ref. 1-3 were each coated withpolydimethylsiloxane having the respective viscosities indicated inTable 4. Samples A-I, E2 and F2 were coated with compositions includingVDT-731 (7.0-8.0% vinylmethylsiloxane)-dimethylsiloxane copolymer,trimethylsiloxy terminated, and/or UMS-182 [15-20%(acryloxypropyl)methylsiloxane]-dimethylsiloxane copolymer, and DC 360polydimethylsiloxane having a viscosity as indicated in Table 4. Eachcomponent was irradiated with cobalt at a dosage specified in Table 4.Each syringe was assembled and filled with 10 ml of deionized water andautoclaved at 124° C. for 30 minutes. The test results reported in Table4 below are an average of the test results for five samples each.

As shown in Table 4, Samples E, F, E2 and F2 according to the presentinvention had low breakloose and sustaining forces. Also, Samples E andF had no sticktion at a pump rate of 10 ml/hr.

TABLE 4 Sample ID Ref 1 Ref 2 Ref 3 A B C D E F G H I E2 F2 FomulationDC 360, 100 25 50 75 75 50 95 90 85 1,000 Cst DC 360, 12,500 Cst DC 360,100 100 75 50 100,000 Cst VDT-731 100 75 50 25 20 40 20 40 (Vinyl)UMS-182 5 10 5 10 15 5 10 (Acrylate) Radiation Dose, kGy 0 45 45 45 4545 45 45 45 45 45 45 45 45 Functional Test Breakout 33/1   24/3   36/0.839/2   44/3   41/2   45/3   27/4   25/2 33/3   30/2   32/1 23/0.8 34/2  force, N Sustaining 5/0.2 5/0.3  7/0.6 8/0.5 7/0.3 6/0.2 7/0.2 5/0.4 6/1 5/0.5 4/0.5  5/1  6/0.6 6/0.4 force, N Pump Test (sticktion: Yes orNo) 10 mL/hr Y Y Y Y Y Y Y Y Y N N Sustaining (reduced) (reduced) force,N 1.0 mL/hr N N Sustaining force, N

The present invention has been described with reference to specificdetails of particular embodiments thereof. It is not intended that suchdetails be regarded as limitations upon the scope of the inventionexcept insofar as and to the extent that they are included in theaccompanying claims.

What is claimed is:
 1. An article of manufacture comprising a firstcomponent having a surface in frictional engagement with a surface of asecond component, at least a portion of at least one surface of at leastone of the first component or the second component being coated with acoating prepared from a composition comprising: (a) a first, curableorganopolysiloxane comprising at least two alkenyl groups, wherein thefirst organopolysiloxane (a) is (7.0-8.0% vinylmethylsiloxane)-dimethylsiloxane copolymer, trimethylsiloxy terminated, and (b) asecond, curable organopolysiloxane comprising at least two polar groups,the second organopolysiloxane being different from the firstorganopolysiloxane, each polar group of the second organopolysiloxane(b) being independently selected from the group consisting of acrylate,methacrylate, amino, imino, hydroxy, epoxy, ester, alkyloxy, isocyanate,phenolic, polyurethane oligomeric, polyamide oligomeric, polyesteroligomeric, polyether oligomeric, polyol, and carboxypropyl, and fluorogroups.
 2. An article of manufacture comprising a first component havinga surface in frictional engagement with a surface of a second component,at least one surface of at least one of the first component or thesecond component being coated with a coating prepared from a compositioncomprising: (a) a first, curable organopolysiloxane comprising at leasttwo alkenyl groups, and (b) a second, curable organopolysiloxane,wherein the second organopolysiloxane (b) is [15-20%(acryloxypropyl)methylsiloxane] - dimethylsiloxane copolymer.